There are two thresholds with LF indexes. First, you have the absolute max. The max is 9999 values. Second, you have the usable limit. This is the value that is open to interpretation and experience. My preference is in the 1500-2000 range. That isn’t an absolute, though, so feel free to play around with this.

I, generally, advise against using HNG indexes, too. Most of this logic is done in other index structures. Also, the other indexes (HG, LF, n-bit) can allow for better performance in terms of parallelism, etc. To be honest, I haven’t done a POC in the last 3+ years where I found that having an HNG index greatly improved performance. Like the LF index threshold, this is open to interpretation and experience. I would say that you try it out to see how your system reacts to having them or not. My experience would show that likely you won’t see significant improvement.